Automatic pilot



March 7,- Y1944. R FINK 2,3143288 AUTOMATIC PILOT 1 Filed may 22. 1942 2sheets-sheet 1 7, R #INK AUTOMATIC PILOT Filed May 22, 1942 2Sheets-Sheet 2 ..........M.mmmmwmmmmmmm @wwwW..........H...............H...

' /A//z/v rauDoLP/J /7/ Af lll l Y Patented Mar. 7,1944

UNITED STATES PATENT OFFICE AUTOMATIC PILOT Rudolph Fink, United StatesArmy,

Patterson Field, Ohio Application May 22, 1942, Serial No. 444,059

6 Claims. (Cl. 244-78) Granted unser the act of March s. is'sajasamended April 30. 1928; 370 0. G. 757) ,control devices which. employ ahorizontal or vertical reference means such as gyroscopes, pendulums andthe like, as a primary control means. `It has been proposed in the priorart to utilize the difference in pressure between points on the upperand lower surfaces of an aircraft wing as a measure of the angle ofattack of the wing with Irespect to the relatively moving air stream andto utilize such a pressure difference in a source of primaiiy controlfor an automatic elevator control. Such a proposed control system,however, cannot ordinarily be employed for actuation of the ailerons orrudder and has the further disadvantage that it would be subject tohunting since there is no way of applying a follow-up from thecontrolled element such as the elevators to cancel the' primary controleii'ect so that the controlled element deilection is proportional to themagnitude of the primary control eect.

In accordance with the present invention a sensitive control element inthe form of a yawmeter head is pivotally .supported om, thesaircraft,preferably on the wing, and adapted to move in a vertical plane forelevator control. s

The yawmeter head is connected to a differential pressure-responsivedevice which is adapted to shift the pilot valve of a hydraulicservomotor position it will not overshoot and cause a hunting about thedesired equilibrium position. By structure as provided in accordancewith the invention it becomes possible to construct an automatic pilotwhich depends only onthe change in angle of attack of the aircraft froma predetermined angle to initiate an elevator control impulse, and bythe provision of a follow-up, a

- stable control system is obtained.

such as now generally employed on automatic pilots, the servomotor beingconnected to actuate the aircraft elevators. The. pivotal mounting forthe vyawmeter headincludes a three-leg differential gear in which' theyawmeter is secured to and rotatable with the carrier-or one leg of thedifferential. A second leg of the differential In order to obtainautomatic directional and lateral control, an exactly similar system isemployed as above described, except that the servomotor is connected tothe ailerons and the yawmeter head is mounted for movement in atransverse plane. 'I'he directional control is accomplished by virtue ofthe fact that in practically all present-day aircraft the aircraft canbe maintained on a straight course by use of the ailerons alone,li. e.banking will produce turning of the aircraft and vice versa any turningwill produce banking or lateral deviation of the aircraft so that anydirectional deviation from a set course as sensed by the directionalyawmeter will produce a lateral banking which will introduce acorrective turning moment, and since any lateral deviation will producea directional change, the control will also act to restore the aircraftto a laterally level position. By rotating the axis of the directionalcontrol yawmeter head laterally with respect to the longitudinal axis ofthe airplane, turns at a substantially constant rate may beaccomplished. Although it is preferred to obtain both lateral anddirectional control through the control of the ailerons, the rudder maybe actuated by the servomotor so that it will be deflected to producethe required turning moments. i

The principalvobject of the invention is the provision of apower-actuated automatic control means for controlling an aircraft aboutat least one of the axes of motion thereof, comprising a pivotallymounted head exposed to the air stream and operative to produce adifferential pressureindicative of any change in the angle is adapted tobe rotated by an electric motor y under manual control so as to alterthe axis of the yawmeter head in the vertical planel with' .respect tothe longitudinal axis of the airplane,

and the third leg of the differential being connected by follow-upcables to the elevator control a motion of the yawmeter head in adirection so -as to cancel the initial control eect so that so thatcontrol movement of the same will cause when the aircraft is restored'to the level flight 56 of the longitudinal axis of the aircraft withrespect to the relatively moving air stream in a given plane from apredetermined angle, and having connected thereto a pressure-responsivemeans responsive to the said differential pressure for controlling servomechanism connected to one of the sets of the aircraft control'surfacesA such as the elevators, the rudder, or the ailerons tocause sdisplacement of the same to restore the aircraft to its predeterminednight attitude with respect to the relative wind and a follow- A pair upconnection between the actuated control sur face and the pivoted headoperative to cause aA movement of said head in the direction towards itsequilibrium position with respect to the relative wind to therebyproduce a stable control system.

Another object of the invention is the provision of an automaticdirectional and lateral control device for aircraft comprising apivotally mounted yawmeter head, a pressure-responsive means actuated bydifferential pressure generated by said head in accordance withdeparture from a predetermined heading with respect to the relativewind, power-actuated servo mechanism connected to the ailerons toactuate the same, control means for said servo mechanism operated by thedifferential pressure-responsive means and a follow-up connectionbetween the ailerons and the said yawmeter head operative to move saidhead in a direction opposite thedirection of aircraft directionaldeviation.

Other objects of the invention will appear by reference to the detaileddescription hereinafter given and to the appended drawings in which:

Figure 1 is a schematic representation 'of an automatic aircraftelevator control system in accordance with the invention;

Figure 2 is an enlarged side elevation illustrating the detailconstruction of the yawmeter control device of Figure 1;

Figure 3 is a top plan view of the device of Figure 2, and; e

Figure 4 is a schematic illustration of the installation of theautomatic control in an airplane for lateral and directional controlthereof.

Referring now to Figure 1, the reference numeral I generally indicates ayawmeter head of a construction per se well known in the art andcomprising a tubular housing 2, which encloses a pair of conduits 3 and4 which terminate at their outer ends. respectively in ports 5 and 6equally angularly spaced on opposite sides of the longitudinal`'centerline of the tubular housing I, and the ports 5 and 6 serving asdynamic pressure openings. The conduits 3 and 4 at their inner ends areconnected by flexible tubes or the y like to conduits 3' and 4 which areconnected yto a pressure-responsive means hereinafter de- 4 scribed. Thetubular housing I is secured at its inner end to .a forked fitting 'Iwhich is movable with the carrier or one leg of athree-leg differentialgenerally indicated by the reference numeral I0 and the details of-whichas seen in Figures 2 and 3 will now be described.

Referring to Figures 2 and 3, the forked support I for the yawmeter headI is boltedto a pair of spaced side plates 8 which are maintained inspaced relation by suitable spacers 9. of spur gears Il and I2 arearranged in spaced relation between the side plates 8 and are securedrespectively to shafts I3 and I4 which are rotatably journalled insuitable bearing bosses formed integral 4with the side. plates 8 andfurther journalled adjacent their -outer ends respectively in bearingsI5 and I6 carried by bracket plates I'I and I8 respectively, which turnmay .be secured for example to the front sparA of an aircraft wing. I

A pair of planetary spur gear pinions and 2l are positioned between theside plates 8 and suitably rotatably .iournalled on-pins carried by theplates, which are so positioned that the gears mesh with each other andrespectively mesh with the side gears Il and I2 to form adiferential.The side gear II and shaft I3 form one suitable source of power andcontrolled by a manually actuated reversing switch, not shown. If themotor 25 is energized to run in either direction and gear I2 and shaftI4 considered as being stationary, then shaft I3 will drive gear Iiwhich will in turn drive planet gears 20 and l 2I causing the lattergear to planetate around gear I2 and carrying side plates 8 therewithand causing the yawmeter head I lto be raised or lowered. In this mannerthe initial angle of the longitudinal centerline of the yawmeter head Iwith respect to a horizontal plane passing through the longitudinal axisof the airplane may be adjusted. The shaft I4 has a pulley 28 mounted onthe outer end thereof vwhich pulley is provided with a cable clamp 29which clamps a follow-up cable 30 to the pulley so as to cause rotationof the same, the upper and' lower branches 30a. and 30h of the cablepassing over respective guide pulleys 32 which are pivotally mounted inbrackets 33 secured as by welding to the mounting plate I5. If thepulley 28 is rotated`in either direction by movement of follow-up cable3i! and gear II being stationary, ro-

` tation of shaftv la win rotate gears 2e and ze 'are secured to amounting plate I9, which iny plates follow-up movement of the head in avertical. to the longitudinal axis of thev causing the latter toplanetate about stationary gear II and thus cause rotation of thecarrier 8 and yawmeter head I to produce a plane relative airplane.

Referring again to Figure 1, the conduits 3' and t are as preyiouslynoted connected to a pressure-responsive device which is indicated bythe reference numeral 35 and being of the double-acting type having acentral diaphragm 36 which divides the housing into two expansiblechambers which respectively connect to the conduits 3' and 4' and thechambers being vented to the atmosphere through restricted air bleeds31. Any increase in pressure in one of the conduits 3' or 4 will causedeection of the diaphragm 36 which will cause displacement of a valverod 38 in the corresponding direction from a n e'utral position andshift a pilot valve 4I yof a, servomotor control valve generallyindicated by the reference numeral 40. Shifting of pilot valve 4I ineither direction from a neutral position, permits oil under pressurefrom a supply conduit 42 to'pass to either one of a pair of conduits 44or 45 and connecting the other.

of the conduits to an exhaust conduit 46. The conduits 44 and 45 areconnected to cpposite. endsvof avservomotor cylinder 48 which has apiston 49 operative to actuate the piston rod 50 in either direction.Piston rod 50 is connected at opposite ends thereof to cables 5I and 52which are connected to'a double arm lever 53A Y alternate ends to theportions 30a. and 30h of the follow-up cable 30, so that any movement ofthe control-surface 54 Vthrough the action. of

servomotor piston 49 will cause a movement of yawmeter head l in adirection to cancel the control pressure created thereby.

' Operation When the device of Figure 1 is installedl in an airplane toaccomplish elevator control, the yawmeter head axis is -adjusted throughdifferential i by energizing motor 25 Vto run in the desired direction,so that the axis of the yawmeter head coincides with the direction ofthe relative wind for the particular air speed and corresponding angleof, attack of the airplane, for example for a selected cruising speed.

, As long as the aircraft illes at the selected air speed, the airstream will strike the dynamic with respect to the relative wind and asthe elevators move in a reverse direction toward the pressure ports 5and 6 so as to produce an equal Apressure in conduits 3 and 4, and nodierential pressure will be produced in the pressure-responsive device35 and the pilot valve 4| will remain in the neutral position, allowingthe oil' under pressure from conduit 42 to ow directly y. to exhaustconduit 46.

If now it is assumed that the aircraft increases its angle of attackwith respect to the relatively moving air stream, the pressure at port 6of the head will increase and the pressure at port 5 will decrease,which will produce a corresponding diiference in pressure in conduits 3and 4'., causing diaphragm 3B of the pressure-responsive device 35 tomove to the right as seen in Figure l, which movementis transmittedtopilot valve 4|. Movement of valve 4| to the right will connect conduit04 to the high-pressure oil supply and vent conduit 45 to drain, the oilunder presi sure in conduit-44 being admitted to servomotor cylinder 48to cause piston 49 to mov'e to the left as seen in Figure l. p Movementof the piston 49 to theleft will, through piston rod 50, tension cable5| to deect the elevators 5t down, which will p'roduce a restoringcontrol forcetending to cause the airplaney to returnk to the'preselected angie of attack. As the elevators y54 are deflecteddownward, piston rod 50 will tension follow-up cable h,4 which willcause pulley 28 and shaft I4 to be rotated in a clockwise direction(Figures 2 and 3) lwhich will cause, through gear Il, a counterclockwiserotation of planet gear 2| and a clockwise rotation of planet gear 20which will roll around stationary gear and rotate carrier plates 8 in a.clockwise sense, the rotation of the latter moving the axis of theyawmeter head downward ltlirough an angle proportional to the deflectionof the elevators 54. The follow-up motion of the yawmeter head may bemade sumcient to entirely cancel the primary control efiect since the.restoring movement of the yawmeter head causes equalization of pressureat ports ,5 and 6 causing a reversal in the direction of movement of thepilot valve and causing the servomotor also to reverse itsmotion. 'Iheoperation of the follow-up is thus such that when the airplane isrestored to its preselected angle of attack, the elevators will berestored to the neutral position and the axis of@ the yawmeter head willagain lbe in its initial position.

When the aircraft, for' example, decreases its angle-oi attack below thepreselected value, the

pressure diiierence created atV ports 5 and B will be of oppositecharacter from that described ,above andthe elevators will be movedupward Ato D cause a down load on the tail of the airplane, causing thesame to restore the aircraft to its predetermined angle of attack. Theaction of neutral position, as the airplane is restored to the correctflying position, the yawmeter head will be rotated in a counterclockwisesense.

'Ihe ratio of the follow-up movement of the yawmeter head to the controlsurface deflection is of course determined by the diameter of thefollow-up pulley 28 (Figure l) as compared to the `stroke of theservomotor piston 40 and this ratio may be made of a value suitable forthe control characteristics of the particular airpplane in question.

'I'he sensitivity of the control system is controlled by the response ofthe diaphragm 38 of the pressure-responsive device 35, Figure l, for agiven pressure dierence between the conduits 3 and 4 (Figure l) and thissensitivity maybe varied by change in the area or elasticcharacteristics of the diaphragm. v

The control system heretofore described as applied to thee longitudinalcontrol of an aircraft is also applicable to the lateral or directionalcontrol of an aircraft, and in order to obtain such a control it is onlynecessary to employ a duplicate of the control system illustrated inFigure 1 and mount the dierential unit and yawmeter head thereof so thatthe latter is movable in a transversce plane, the servomotor beingconnected to control the ailerons in a well-known manner.

The arrangement of the parts for directional control is illustrated inFigure 4, in which gure the equivalent parts to the device of Figure lare indicated by the same reference numeral plus one hundred. As seen inFigure 4 the yawmeter head |0| having dynamic pressure ports |05 and |00is mounted, for example on the airplane wing or fuselage, for movementlaterally and adapted to be actuated by the diilerential unit ,I I0 inthe same manner as in the device of Figure l and the initial position ofthe yawmeter head is determined by operation of motor |25 through asuitable manually controlled switch, not shown, and a suitableindicator, also not shown, operated by movement of the yawmeter head maybe employed to indicate the angular position of the longitudinal axis ofthe head with respect to the longitudinal axis of the airplane. Theyawmeter head has its dynamic pressure ports |05 and |06 connected tothe valve operating pressure-responsive device |35 by conduits |03' and|04' and the motor |35 is adapted to actuate pilot valve |40 which inturn controls the servomotor |48 in the same manner as in the system ofFigure 1. The servomotor |48 has its piston rod |50 connected to thecables |5| and |52 which in turn are adapted to actuate bell cranks |6|and |52 respectively of a conventional aileron control system foractuating the ailerons |53 and |54 respectively in opposite directions,

the latter also being adapted to be controlled in Operation The deviceof Figure e, when employed to maintain the associated aircraft on apredetermined course is initially set by the pilot through operation ofthe motor E25 so that the axis of the yawmeter head im is aligned withthe longitudinal axis of the aircraft after the latter has been placedon the proper heading. If thereafter the aircraft should yaw to theleft,there will be an increase in dynamic pressure at port it@ which willcause pressure-responsive device E35 to actuate valve it@ to the right,which will in turn cause operation of the piston of servornotoi` idd tothe left causing aileron ld to move up and aileron it@ to move down.

It is a well-known fact that in aircraft which do not have excessivedirectional stability, a yawing moment is also accompanied by a rollingmoment and vice versa, and an aircraft can be controlled both laterallyand directionaily by use of Y the ailerons alone and in the presentinvention the aileron movement as above described will produce a rollingmoment tending to raise the low wing and which will cancel the yawingmoment, thus restoring the aircraft to its original heading. Themovement of the ailerons produces a follow-up movement of the yawmeterhead lidi towards the right which cancels the control signal andreverses the direction of movement of the servometer so that the ailerondeflection is proportional to the instant deviation in yaw and as theaircraft is laterally restored to the level position, the aileronsreturn to the neutral position and the yawmeter head is again inalignment with the longitudinal axis of the aircraft.

When the aircraft yaws to the right, the automatic control operates in areverse sense from that as above described.

When the pilot desires to make a change in course, for example, tol turnleft (looking forward as seen in Figure d), the pilot, through manualcontrol of motor E25, causes the yawmeter head tdi to move to the rightan amount dependent upon the desired radius 'of turn for` the thenexisting air speed, and upon the yawmeter head being so deflected therewill be an increase in the dynamic pressure at port 35 which will causethe pressure-responsive device 435 to shift the valve E50 to the left.which will cause a movement of the servomotor idd in the oppositedirection. The aileron H53 will be caused to move up and aileron 664 tomove down, thus banking the aircraft in a counterclockwise sense whichwill cause the aircraft to turn to the left.- As the airplane banks, thefollow-up motion of the yawmeter head is to the left tending to restorethe same to its' initial position, also causing the ailerons to move tothe neutral position and leaving the aircraft banked the desired amount,so that it will continue to turn at a constant rate for any given airspeed. The turn may be stopped by operation of the electric motor i25ina reverse sense an equal amount, and the reverse operation of theailerons will take place restoring the aircraft to the laterally levelposition and with the yawmeterhead again aligned with vthe longitudinalaxis of the airplane.

Lateral tilting of the aircraft in either direction will cause theaircraft to'turn either to the right or left from the desiredpredetermined course, which turning will set the directional controlinto operation to cancel the turning moment by applying the oppositeaileron which will result in the aircraft being restored to thelaterally level position so that the automatic control system ofmovement thereof, reversible servomotor rneansA operatively connected toa control element of the aircraft, control means for said servomotoradaptved to cause selective actuation of said servomotor,

pivotally supported means exposed to lthe air stream and adapted togenerate a dierential pressure proportional to the change in attitude ofthe aircraft from a predetermined attitude with respect to the relativeair stream, pressure? responsive means responsive to differentialpressures generated by said last named means, said pressure-responsivemeans being operatively connected to said servomotor control means tocause selective actuation of the same and follow-up means operativelyconnecting said servomotor and vsaid pivotally supported means to causea rotation of the latter in a. direction opposite the deviation. of theaircraft from the said predetermined attitude.

2. Means for automatically actuating a control surface of an aircraftcomprising a reversible servomotor connected to said surface to actuatethe same, control means for said servomotor to cause selective actuationthereof, dierentialpressure-responsive means operatively connected to'said servomotor control means to selectively actuate the control means,a rotatably mounted longitudinally extending head exposed to a.relatively moving air stream and having a pair-of dynamic pressure portsequally angularly disposed wth respect to the longitudinal axis of saidhead, connections between said ports and saiddifferential-pressure-responsive means, and fol low-up means operativeto rotate said rotatably mounted headin response to movement of saidcontrol surface by said servomotor and in a direction tending tomaintain the longitudinal axis of said head parallel with the relativelymoving air stream.

3. In an automatic elevator control for an aircraft, a. reversibleservomotot for actuating the elevators of the aircraft to restore theaircraft to a predetermined attitude with respect to the relative wind,a control element for selectively controlling the energizing of saidservomotor, differential-pressure-responsive means for actuating saidcontrol element, a yawmeter head eposed to the air stream and having a.pair of dya namic pressure ports equally angularly disposed above andbelow the longitudinal axis of said head and said ports beingrespectively connected to vsaid pressure-responsive means so that thelatter is caused to be actuated in one or the other control sense uponincrease or decrease respectively in the pressure in one of said portsover the pressure in the other of said ports upon change in the aircraftflight attitude in one or the other direction from a predeterminedattitudewith respect to the relative wind, means for pivotallysupporting said yawmeter head for rotary movement in a vertical plane,and follow-up means responsive to movement of Ithe control surface andconnected to said yawmeter head to cause a rotation thereof tending tomaintain said head parallel with the relatively moving air stream.

4. The structure as claimed in claim 3, in which means are providedindependent of said followup means for manually rotating said yawmeterhead to a preselected angle with respect to the longitudinal axis of theassociated aircraft.

5. An automatic lateral and directional control for an airplanecomprising, a reversible servomotor, operative connections between theservomotor and the airplane ailerons to actuate the same, selectivecontrol means for said servomotor, differential-pressure-responsivemeans for actuating said control means, a yawmeter head pivotallysupported for lateral movement to either side of a central positionparallel to the longitudinal axis of the associated airplane and exposedto a relatively moving air stream, said yawmeter head including a pairof dynamic pressure openings equally angularly disposed in a horizontalplane with respect to the longitudinal axis of said head, fluid pressuretransmitting connections between said dynamic pressure openings and saiddiierential-pressure-responsive device whereby differences in dynamicpressure at said openings are operative to cause selective operation ofsaid servomotor control means and a follow-up responsive to operation ofsaid servomotor to cause rotation of said yawmeter head in a directiontending to equalize any difference in pressure between said dynamicpressure openings due to yaw of the airplane With'respect to therelatively moving air stream.

6. The structure as claimed in claim 5, including manually controlledmeans for rotating the longitudinal axis of said yawmeter head to make adesired lateral angle with respect to the longitudinal axis of theassociated airplane.

RUDOLPH FINK.

